Thermostatic switch



Jan. 24, 1956 R. FONT THERMOSTATIC SWITCH Filed Feb. 5, 1955 IGE FIG.1

INVE'NTOR. RA M0 N F ON T AL/MAL United States Patent THERMOSTATIE SWITCH:

Ramon Font, Richmond Hill, N. Y.,, assignor to Premier Research Laboratories, Inc., New York, N. L, a corporation of New York Application February 3,, 1955, Serial No. 485,886

4 Claims. (Cl'. 200-138) This invention. relates. to thermostatic switches, and more particularly to an. improved thermostatic switch. of the bimetal type.

A main object of the invention is; to provide an improved adjustable thermostatic switch whichv is simple in construction, WhiCiLiS reliable in operation, and which may be accurately adjusted to open or close its contacts at a predetermined temperature;

A further object. of the invention is. to. provide an improved thermostatic switch of the type actuated by a bimetal heat-responsive. element, the switch. being arranged so that. the bimetal element is not. employed to carry any appreciable. amount of. current, whereby said element is not affected to any substantial degree by the heating effect of current. passing therethrough, the: thermostatic switch being inexpensive to manufacture, being rugged in construction, and being, very compact in size.

Further objects and advantages of the invention will become apparent from the. following description and claims, and from the: accompanying drawings, wherein:

Figure 1 is a top plan view of a circular wall member on which is mounted an improved adjustable thermo- Referring to the drawings, and more particularly to Figures 1 and 2, 11 designates a Wall element, which may comprise a portion of a temperature-controlled enclosure, such as a crystal oven, or other enclosure provided with an electrical heating Winding whose energization is to be controlled so as to maintain a desired temperature in the enclosure. The wall element 11 is of suitable insulating material, such as plastic or the like.

Designated at 12 is a first resilient contact arm which is secured to wall element 11 at one end portion thereof, as by metal eyelets 13, 13, one of which may be employed as a terminal of the switch. Conductively secured on the top surface of the other end portion of arm 12 is a contact element 14. Threadedly engaged through wall element 11 below said other end portion of arm 12 and beneath contact element 14 is the adjusting screw 15, which may be rotated to adjust the normal elevation of contact element 14 with respect to wall element 11.

Designated at 16 is a second resilient contact arm which is secured to wall element 11 at right angles to contact arm 12, as shown, as by a pair of metal eyelets 17, 17, one of which may be employed as a terminal of the switch. The eyelets 17 extend through a metal spacer all) ice

block. 18 and through the end portion ofa bimetal strip 19 arranged: beneath. the resilient contact arm 16. The bimetalv strip 19 extends a: substantial distance toward the free end of contact arm 16.

The free end of. contactiann. 16 overlies. the contact element 14.. Securedto the underside of. said free end, parallel to contact element. 14,. is. a cooperating contact element. 20.

The intermediate portion of contact arm 16 is formed with a depending conical indentation 21 of substantial size and having a. relatively sharply pointed bottom tip which engages the free end. portion. of the bimetal strip 19. The conical indentation 21 spaces the: main portion of the contact arm 16 away from the bimetal strip 19 and serves. as a means for transmitting movement of the end portion of the bimetal: strip to the resilient contact arm 16. Saidindentation is continuously biased into contact with the bimetal strip by the resiliency of contact arm 16.

When the bimetal strip 19 flexes downwardly, due to falling temperature in the enclosure being controlled, contact element 20 engages contact element 14, allowing heater current. to flow through arm 12, contact 14, contact 20, and arm 16. Since the tip of indentation 21 makes only point contact with the bimetal strip 19, whereby there is a relatively high. contact resistance. between said tip and the bimetal strip, practically none of the heater current flows through the bimetal strip, the major part of: the heater current passing through the. contact arm 16.

Therefore, the bimetalstrip is alfected substantially only by the ambient temperature. in the enclosure, although it is in positive contact with the resilient contact arm 16 and. governs: the flexure of said contact arm.

When the ambient temperature rises to a predetermined value, controlled by the setting of the regulating screw 15, the bimetal strip 19 flexes upwardly sufficiently to separate contact element 20 from contact element 14, whereby the. heater current: is interrupted and the heater winding becomes dcene'rgized.

Referring now to the form of the invention illustrated in Figures 3 to 6, 22 designates a. main supporting body of suitable insulatingmaterial, such as porcelain, or the like. Body 22 is rodlike in shape. andis formed with the top and bottom channels: 23 and 24, separated by a horizontal web 25, as illustrated.

Designated. at 26. is a flat metal plate member secured in one end portion of bottom channel 24 by: eyelets; 27, 27 one of which may be employed as a terminal of the switch. As shown, plate member 26 projects a substantial distance beyond the forward end of body 22. Threaded through the forward end portion of plate member 26 is the adjustable vertical contact screw 28.

The forward end of plate 26 is formed with slot 29 communicating with the tapped opening containing screw 28, to insure easy adjustment of the screw.

Designated at 30 is a resilient contact arm which is secured at its rear end portion to the rear portion of the top channel 23, as by the eyelets 31, 31 extending through web element of body 22. As shown, the forward portion of arm overlies contact screw 28 and has secured to its underside a contact element 32 which is conductively engageable with said contact screw. The rear end of arm 30 extends beyond the rear end of body 22 and is apertured at 33 to define a switch terminal.

interposed between arm 30 and the bottom wall of top channel 23 are the spacer block 34 and the bimetal strip 35, the eyelets 31 extending through these members, as shown. Bimetal strip 35 underlies a substantial portion of arm 30 and is spaced therefrom at its free end portion by a depending conical indentation 36 in the arm 30. As in the previously described form of the invention, indentation 36 is of substantial size and has a relatively sharp bottom tip, making substantially point contact with the subjacent surface of bimetal strip 35.

As in the previously described embodiment of the invention, movement of the free end portion of bimetal strip 35 is transmitted directly to the resilient contact arm 30 through the conical indentation 36, whereby the heater circuit to which the switch is connected will be opened or closed at a predetermined temperature, controlled by the setting of contact screw 28. Because of the high contact resistance between the point of indentation 36 and the surface of the bimetal strip 35, practically the entire heater current flows through the contact arm 30 and very little current flows through the bimetal strip.

The conical indentation in the resilient contact arm may be readily formed by means of a suitable indenting punch and die set, and involves negligible manufacturing expense. The use of said indentation enables straight bimetal strips to be employed in the units, and since no deformation of the bimetal strips is required, this reduces the unit cost of the assembly as over previously known thermostatic switches of the bimetal type.

While certain specific embodiments of thermostatic switches of the bimetal'type have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

What is claimed is:

1. A thermostatic switch comprising a support, a first contact member mounted on said support, a resilient contact arm secured to said support and overlying said first contact member, a bimetallic, temperature-responsive strip secured to said support in contact with and underlying said contact arm, and a depending conical indentation formed in said resilientlcontact arm, said conical indentation having a relatively sharp bottom tip engaging said bimetallic strip and urged thereagainst by said arm, whereby said contact arm.will be flexed in accordance with the fleXure of said bimetallic strip.

2. Athermostatic switch: comprising a support, a first contact member mounted on. said support, first terminal means on said support electrically .connected to said first contact member, a resilient contact arm overlying said first contact member a bimetallic, temperature-responsive strip in contact with and underlying said resilient contact arm, common fastening means securing end portions of said contact arm and bimetallic strip remote from said first contact member to said support, a depending conical indentation formed in said resilient contact arm and having a relatively sharp bottom tip engaging said hi metallic strip with substantially point contact and urged thereagainst by said arm, whereby said contact arm will be flexed in accordance with the flexure of said bimetallic strip, and second terminal means on said support electrically connected to said resilient contact arm at said common fastening means.

3. A thermostatic switch comprising a support, a first contact member mounted on said support, screw means formed and arranged to adjust the elevation of said first contact member with respect to said support, first terminal means on said support electrically connected to said first contact member, a resilient contact arm overlying said first contact member, a bimetallic, temperature-responsive strip in contact with and underlying said resilient contact arm, common fastening means securing end portions of said contact arm and bimetallic strip remote from said first contact member to said support, a depending conical indentation formed in said resilient contact arm and having a relatively sharp bottom tip engaging said bimetallic strip with substantially point contact and urged thereagainst by said arm, whereby said contact arm will be flexed in accordance with the flexure of said bimetallic strip, and second terminal means on said support electrically connected to said resilient contact arm at said common fastening means.

4. A thermostatic switch comprising a generally channel-shaped body of insulating material, a first contact member secured to one end of said body, screw means formed and arranged to adjust the elevation of said first contact member with respect to said body, first terminal means on said body electrically connected to said first contact member, a resilient contact arm disposed in the channel of said body and overlying said first contact member, a bimetallic temperature-responsive strip in contact with and underlying said resilient contact arm, common fastening means securing end portions of said contact arm and bimetallic strip remote from said first contact member to said body, a depending conical identation formed in saidresilient contact arm and having a relatively sharp bottom tip engaging said bimetallic strip with substantially point contact and urged thereagainst by said arm, whereby said contactarm will be flexed in accordance with the flexure of said bimetallic strip, and second terminal means on said body electrically connected to said resilient contact arm at said common fastening means.

Smith et al. Dec. 28, 1937 I Swenson Oct. 31, 1950 

